In vitro hydrolysis rate and protein binding of clevidipine, a new ultrashort-acting calcium antagonist metabolised by esterases, in different animal species and man

Drug and pro-drug substrates and pseudo-substrates of human butyrylcholinesterase

Butyrylcholinesterase (BChE) is present in plasma and numerous cells and organs. Its physiological function(s) is(are) still unclear. However, this enzyme is of pharmacological and toxicological importance. It displays a broad specificity and is capable of hydrolyzing a wide range of substrates with turnovers differing by several orders of magnitude. Nowaday, these substrates include more than two dozen carboxyl-ester drugs, numerous acetylated prodrugs, and transition state analogues of acetylcholine. In addition, BChE displays a promiscuous hydrolytic activity toward amide bonds of arylacylamides, and slowly hydrolyzes carbamyl- and phosphoryl-esters. Certain pseudo-substrates like carbamates and organophosphates are major drugs of potential medical interest. The existence of a large genetic poly-allelism, affecting the catalytic properties of BChE is at the origin of clinical complications in the use of certain drugs catabolized by BChE. The number of drugs and prodrugs hydrolyzed by BChE is expected to increase in the future. However, very few quantitative data (Km, kcat) are available for most marketed drugs, and except for myorelaxants like succinylcholine and mivacurium, the impact of BChE genetic mutations on catalytic parameters has not been evaluated for most of these drugs.

Simultaneous Quantitation of Clevidipine and Its Active Metabolite H152/81 in Human Whole Blood by LC-MS/MS: Application to Bioequivalence Study

Clevidipine is an ultrashort-acting dihydropyridine calcium antagonist, which can control blood pressure accurately. It is necessary to develop a liquid chromatography–tandem mass spectrometry (LC-MS/MS) method to quantitate clevidipine and its active metabolite H152/81 for clinical pharmacokinetic study and therapeutic drug monitoring. Liquid–liquid extraction was used for sample preparation, and clevidipine-d7 and H152/81-13C-d3 were chosen as the isotope internal standard. The chromatographic separation was performed on an ACE Excel 2 Phenyl column (50 × 2.1 mm). Mass quantification was carried out on the multiple reaction monitoring of the transitions of m/z 473.1→338.1, 480.1→338.1, 356.0→324.0, and 362.2→326.2 for clevidipine, clevidipine-d7, H152/81, and H152/81-13C-d3. The validated method gave an excellent linearity over a concentration range of 0.1–30 ng/ml for clevidipine and 2–600 ng/ml for H152/81. Other fully validated content such as accuracy, precision, extraction recovery, matrix effect, and stability were also investigated and showed satisfactory results. It was strongly recommended that whole blood is the first choice for clinical bioanalysis. Using whole blood for sample analysis can reduce the whole blood collection volume (1 ml vs. 4 ml) and shorten the time from sample collection to storage to 5 min, and there is no centrifugation process and precooling in the ice water bath, which can further reduce the instability caused by exposure. The method was successfully applied to a bioequivalence study of clevidipine butyrate-injectable emulsion.

The Current Role of Clevidipine in the Management of Hypertension

Acute hypertension, which may damage blood vessels, causes irreversible organ damage to the vasculature, central nervous system, kidney, and heart. Clevidipine, the first third-generation calcium channel antagonist approved by the Food and Drug Administration (FDA) in the past 20 years, is an ultra-short-acting calcium channel blocker that inhibits L-type calcium channels with high clearance and low distribution, can be rapidly metabolized into the corresponding inactive acid, and is rapidly hydrolyzed into inactive metabolites by esterase in arterial blood. Clevidipine is the same as nicardipine in that the main physiological effect is vasodilation and the main target is the arterial system, which has a limited effect on capacitor vessels. Unlike nitroglycerin, clevidipine has a limited effect on preload. In contrast to other direct-acting vasodilators, clevidipine has an ultra-short half-life due to metabolism by nonspecific blood and tissue esterases. Clevidipine trials conducted in adult populations have proven that it can rapidly control blood pressure in cardiac surgery situations and that adverse reactions to clevidipine are similar to those with other antihypertensive agents. In recent years, clinical trials have shown that clevidipine has excellent blood pressure-lowering capability in patients with acute neurological injury (hemorrhage, stroke, and subarachnoid and acute intracerebral hemorrhage), those  undergoing coronary artery bypass graft or spinal surgery, and in those with cerebral aneurysm/pheochromocytoma, acute heart failure, acute aortic syndromes, or renal insufficiency with severe hypertension, and it is equivalent to commonly used blood pressure-lowering medicines such as nicardipine or nitroglycerin. However, there is a lack of large-scale clinical trial data on the efficacy and safety of clevidipine in children during the perioperative period.

Interspecies differences in stability kinetics and plasma esterases involved in hydrolytic activation of curcumin diethyl disuccinate, a prodrug of curcumin

The investigation of in vitro plasma metabolism of ester prodrugs is an important part of in vitro ADME assays during preclinical drug development. Here, we show that the in vitro metabolism including plasma stability and metabolizing enzymes of curcumin diethyl disuccinate (CDD), an ester prodrug of curcumin, in dog and human plasma are similar but markedly different from those in rat plasma. HPLC and nonlinear regression analyses indicated that the hydrolysis of CDD in plasma followed a consecutive pseudo-first order reaction. The rapid hydrolytic cleavage of CDD in rat, dog, and human plasma was accelerated by plasma esterases in the following order: rat ≫ human > dog. LC-Q-TOF/MS analysis showed that the cleavage of ester bonds of CDD is preferential at the phenolic ester. Monoethylsuccinyl curcumin is the only intermediate metabolite found in plasma metabolism of CDD in all tested species. Further investigation using different esterase inhibitors revealed that carboxylesterase is the major enzyme involved in the hydrolysis of CDD in rats while multiple plasma esterases play a role in dogs and humans. Thus, the difference in the hydrolysis rates and the metabolizing enzymes of CDD metabolism in rat, dog and human plasma observed here is of benefit to further in vivo studies and provides a rationale for designing ester prodrugs of CUR with esterase-specific bioactivation.

Conversion and pharmacokinetics profiles of a novel pro-drug of 3-n-butylphthalide, potassium 2-(1-hydroxypentyl)-benzoate, in rats and dogs

Potassium 2-(1-hydroxypentyl)-benzoate (dl-PHPB) is a novel pro-drug of 3-n-butylphthalide (dl-NBP) that is used to treat ischemic stroke. Currently, dl-PHPB is in phase II-III clinical trials in China. In this study, we investigated the conversion and pharmacokinetics profiles of dl-PHPB in vitro and in vivo. The conversion of dl-PHPB to dl-NBP was pH- and calcium-dependent, and paraoxonase was identified as a major enzyme for the conversion in rat plasma. The pharmacokinetics, tissue distribution and excretion of dl-PHPB were studied and compared with equal-molar doses of dl-NBP in rats and dogs. The in vivo studies showed that dl-PHPB could be quickly and completely converted to dl-NBP. The plasma concentration-time course of converted dl-NBP after intravenous dl-PHPB administration was nearly the same as that after equal-molar dl-NBP. The C_max and AUC of dl-NBP after oral dl-PHPB administration in rats and dogs were higher by 60% and 170%, respectively, than those after oral dl-NBP administration. Analysis of the tissue distribution of dl-PHPB revealed that converted dl-NBP was primarily distributed in fat, the brain and the stomach. In the brain, the levels of dl-NBP were relatively higher after dl-PHPB treatment by orally than after treatment with equal-molar dl-NBP. Approximately 3%-4% of dl-NBP was excreted within 72 h after dosing with dl-PHPB or dl-NBP, but no dl-PHPB was detected in urine or feces excrements. Our results demonstrate that the conversion of dl-PHPB is fast after oral or intravenous administration. Furthermore, the bioavailability of dl-PHPB was obviously better than that of dl-NBP.

Perioperative Use of Clevidipine: A Systematic Review and Meta-Analysis

Background

Clevidipine is an ultrashort-acting drug for rapid reduction of blood pressure by selectively acting on the L-type Ca2+ channels on arteriolar smooth muscle. The drug’s ultrashort action in reducing the blood pressure is due to its rapid hydrolysis by blood and extravascular tissue esterases, which does not depend on hepato-renal metabolism and excretion. An analysis of the perioperative management of blood pressure should be considered to compare with other intravenous antihypertensive agents.

Methods

Analyses of the available evidence in randomized clinical trials following the PRISMA methodology as well as clinical significance according to the GRADE system were conducted. Placebo versus other antihypertensive drugs studies were included. Statistical assessments were done using the X2 and I2 tests.

Results

Clevidipine was more effective in maintaining the blood pressure within pre-specified ranges compared with other antihypertensive drugs (MD, -17.87 CI 95%: -29.02 to -6.72; p = 0.02). The use of Clevidipine versus placebo and rescue antihypertensive intravenous drug showed a clear reduction in rates of treatment failure (RR 0.10; IC 95%; 0.05–0.18; p <0.0001). There was no difference in the incidence of adverse events compared with placebo (RR 1.47; 95% CI 0.89 to 2.43, p = 0.14) and with other antihypertensive drugs (RR 0.78, 95% CI 0.45 to 1.35; p = 0.37). In addition, there was no difference in the incidence of atrial fibrillation (AF) between clevidipine and control groups (RR 1.09, IC del 95%: 0.65 a 1.83; p = 0.73).

Conclusions

Clevidipine is an ultrafast-acting drug that is highly effective for management of perioperative arterial hypertension. It is devoid of adverse effects associated with the use of other IV antihypertensives. Its favorable pharmacodynamic and pharmacokinetic properties make clevidipine the drug of choice for the management of acute perioperative hypertension. It is important to emphasize the need for further studies with a larger number of patients to confirm these findings and increase the degree of evidence.

Clevidipine: a review of its use for managing blood pressure in perioperative and intensive care settings

The ultrashort-acting dihydropyridine calcium channel antagonist clevidipine (Cleviprex(®)) has a rapid onset and offset of effect and reduces blood pressure (BP) by decreasing arteriolar resistance without affecting venous capacitance vessels. This article reviews the clinical efficacy and tolerability of intravenous clevidipine when used to manage BP in perioperative and intensive care settings, as well as summarizing its pharmacological properties. Intravenous clevidipine effectively treated preoperative and postoperative hypertension in patients undergoing cardiac surgery, according to the results of the randomized, multicentre, double-blind, phase III ESCAPE-1 and ESCAPE-2 trials. The randomized, open-label, multicentre, phase III ECLIPSE trials indicated that in terms of keeping systolic BP within the target range, clevidipine was more effective than nitroglycerin or sodium nitroprusside perioperatively and had similar efficacy to nicardipine postoperatively in cardiac surgery patients. In small, double-blind trials in patients undergoing coronary artery bypass graft surgery, perioperative clevidipine was noninferior to nitroglycerin, and postoperative clevidipine had similar efficacy to sodium nitroprusside. Noncomparative studies demonstrated that clevidipine provided rapid BP control in patients with acute neurological injuries (including intracerebral haemorrhage, subarachnoid haemorrhage and acute ischaemic stroke), and was not associated with 'overshoot' in the vast majority of patients. Intravenous clevidipine was generally well tolerated and was usually associated with no reflex tachycardia or only very modest increases in heart rate. In conclusion, intravenous clevidipine is a valuable agent for the management of BP in perioperative and intensive care settings.

Screening of stabilizers for LC–MS/MS analysis of clevidipine and its primary metabolite in dog whole blood

Background: Clevidipine is an ester-containing antihypertensive agent that undergoes rapid hydrolysis in blood. A reliable stabilizer cocktail containing citric acid and ascorbic acid was established and the LC–MS/MS method was validated for simultaneous determination of clevidipine and its major metabolite in beagle dog whole blood. Results: The stabilizer could nearly completely inhibit the esterase activity. Both analytes were extracted from whole blood by toluene and detected by MS/MS in positive ESI mode. The linearity range was 0.1–100.0 ng/ml for clevidipine and 1.0–1000.0 ng/ml for the primary metabolite. Conclusion: The stabilizer cocktail was able to effectively suppress the activity of esterase in blood. The method was successfully applied to a PK study of clevidipine in beagle dogs.

Analysis of species-dependent hydrolysis and protein binding of esmolol enantiomers

The stereoselective hydrolysis of esmolol in whole blood and in its separated components from rat, rabbit and human was investigated. Blood esterase activities were variable in different species in the order of rat>rabbit>human. Rat plasma showed the high esterase activity and had no stereoselectivity to enantiomers. Rabbit red blood cell (RBC) membrane, RBC cytosol and plasma all hydrolyzed esmolol but with different esterase activity, whereas the hydrolysis in RBC membrane and cytosol showed significant stereoselectivity towards R-(+)-esmolol. Esterase in RBC cytosol from human blood mainly contributed to the esmolol hydrolysis, which was demonstrated with no stereoselctivity. Esterase in human plasma showed a low activity, but a remarkable stereoselectivity with R-(+)-esmolol. In addition, the protein concentration affected the hydrolysis behavior of esmolol in RBC suspension. Protein binding of esmolol enantiomers in human plasma, human serum albumin (HSA) and α1-acid glycoprotein (AGP) revealed that there was a significant difference in bound fractions between two enantiomers, especially for AGP. Our results indicated that the stereoselective protein binding might play a role in the different hydrolysis rates of esmolol enantiomers in human plasma.

Pharmacokinetics, pharmacodynamics, and safety of clevidipine after prolonged continuous infusion in subjects with mild to moderate essential hypertension

Purpose

Clevidipine is a rapidly-acting intravenous dihydropyridine antihypertensive acting via calcium channel blockade. This was a randomized, single-blind, parallel-design study of a 72-h continuous clevidipine infusion.

Method

Doses of 2, 4, 8, or 16.0 mg/h or placebo were evaluated in 61 subjects with mild to moderate essential hypertension. IV clevidipine or placebo was initiated at 2.0 mg/h and force-titrated in doubling increments every 3 min to target dose, then maintained for 72 h. Blood pressure and heart rate were measured during infusion, and for 4, 6 and 8 h after termination of infusion, although oral therapy could be restarted at 4 h. Clevidipine blood levels were obtained during infusion and for 1 hour after termination.

Results

Rapid onset of drug effect occurred at all clevidipine dose levels, with consistent pharmacokinetics and rapid offset after 72-h infusion. No evidence of tolerance to the clevidipine drug effect was observed at any dose level over the 72-h infusion. No evidence of rebound hypertension was found for either 4 or 6 h after termination of the clevidipine infusion. At 8 h following cessation of clevidipine, blood pressure was not significantly higher than at baseline. Placebo-treated subjects had blood pressures lower than baseline at 8 h following infusion termination; hence, placebo-adjusted blood pressures tended to be slightly higher than baseline.

Conclusion

This study supports the use of up to 72 h of IV clevidipine therapy for the management of blood pressure, with consistent pharmacokinetic/pharmacodynamic characteristics and context insensitive half-life across the dose ranges evaluated.

Hypertensive emergencies: an update

PURPOSE OF REVIEW

Systemic hypertension (HTN) is a common medical condition affecting over 1 billion people worldwide. One to two percent of patients with HTN develop acute elevations of blood pressure (hypertensive crises) that require medical treatment. However, only patients with true hypertensive emergencies require the immediate and controlled reduction of blood pressure with an intravenous antihypertensive agent.

RECENT FINDINGS

Although the mortality from hypertensive emergencies has decreased, the prevalence and demographics of this disorder have not changed over the last 4 decades. Clinical experience and reported data suggest that patients with hypertensive urgencies are frequently inappropriately treated with intravenous antihypertensive agents, whereas patients with true hypertensive emergencies are overtreated with significant complications.

SUMMARY

Despite published guidelines, most patients with hypertensive crises are poorly managed with potentially severe outcomes.

Clevidipine : a state-of-the-art antihypertensive drug under the scope

INTRODUCTION

Clevidipine butyrate is the first intravenous antihypertensive drug to be approved by the FDA over the last decade. This medication is approved for use in the USA, Australia and New Zealand, but is still pending for approval in Europe. It is a new agent that might change the current management for severe acute hypertension in the critical care, emergency and perioperative areas.

AREAS COVERED

This systematic review summarizes the pharmacological and clinical characteristics of this third-generation dihydropyridine intravenous calcium channel blocker, and was done using the literature available from the first publication in 1999 up until now, including the pivotal trials that led to its approval.

EXPERT OPINION

This agent is arterially selective, has an ultrashort half-life, with no CYP-mediated interactions with other medications and is easily titratable. These characteristics place it in a unique category compared with other commonly used antihypertensives. Clevidipine butyrate reaches target systolic blood pressure in more than 90% of patients, within 30 min. It has a low incidence of adverse reactions and is generally well tolerated. The main goal of this review is to provide healthcare providers with a comprehensive appraisal of this promising medication.

In vitro stability and metabolism of O2', O3', O5'-tri-acetyl-N6-(3-hydroxylaniline) adenosine in rat, dog and human plasma: chemical hydrolysis and role of plasma esterases

O2', O3', O5'-tri-acetyl-N(6)-(3-hydroxylaniline)adenosine (WS070117), a new structure-type lipid regulator, is being developed in pre-clinical study. In order to monitor drug kinetics it is essential to understand pre-analytical factors that may affect drug assay. In vitro stability and metabolism were investigated using high-performance liquid chromatography (HPLC) method in this study. The hydrolysis products were identified by HPLC-mass spectrometry (MS)/MS method. The esterases involved in WS070117 hydrolysis was assigned via inhibition rate assay. It was found that WS070117 was chemically unstable in alkaline solutions compared to acidic and near neutral solutions. Enzymatic hydrolysis was even more rapid. Hydrolytic rate constants differ between species, being 4.24, 5.96 × 10(-3) and 6.85 × 10(-2) min(-1) in rat, dog and human plasma at 37°C, respectively. The hydrolysis was catalyzed by plasma esterase because NaF (sodium fluoride: a general esterase inhibitor) inhibited WS070117 hydrolysis and metabolite production. Hydrolysis was fast in rat plasma and was catalysed by carboxylesterase and butyrylcholinesterase. In dog plasma, carboxylesterase, butyrylcholinesterase and paraoxonase were mainly responsible. Butyrylcholinesterase was the major esterase involved in WS070117 hydrolysis in human plasma. The WS070117 hydrolysis in plasma proceeded by gradual loss of acetyl groups. The knowledge of in vitro drug stability and metabolic pathways identified in this study will be essential for future pre-clinical and clinical pharmacokinetics studies.

Role of clevidipine butyrate in the treatment of acute hypertension in the critical care setting: a review

Acutely elevated blood pressure in the critical care setting is associated with a higher risk of acute end-organ damage (eg, myocardial ischemia, stroke, and renal failure) and perioperative bleeding. Urgent treatment and careful blood pressure control are crucial to prevent significant morbidity. Clevidipine butyrate (Cleviprex) is an ultrashort-acting, third-generation intravenous calcium channel blocker. It is an arterial-selective vasodilator with no venodilatory or myocardial depressive effects. Clevidipine has an extremely short half-life of approximately 1 minute as it is rapidly metabolized by blood and tissue esterases. These metabolites are then primarily eliminated through urine and fecal pathways. The rapid onset and the short duration of action permit tighter and closer adjustment of the blood pressure than is possible with other intravenous agents.

Clevidipine for the treatment of severe hypertension in adults

BACKGROUND

Intravenous antihypertensive agents are used when immediate control of blood pressure (BP) is required, including during the perioperative cardiac surgery period. Controlling postoperative BP is challenging because of the need to adequately reduce BP while maintaining appropriate end-organ perfusion. Clevidipine is an intravenous, ultra-short-acting, third-generation dihydropyridine calcium channel antagonist with selectivity for arteriolar vasodilatation. It is approved by the US Food and Drug Administration for the treatment of severe hypertension.

OBJECTIVE

This paper reviews the clinical pharmacology, pharmacokinetic and pharmacodynamic properties, tolerability, and clinical efficacy of clevidipine.

METHODS

To minimize selection bias, each author conducted an independent search for English-language publications indexed on MEDLINE and International Pharmaceutical Abstracts through January 2010 using the term clevidipine. All identified prospective, randomized and nonrandomized Phase III trials were included in the review.

RESULTS

Seven Phase III trials were identified in which clevidipine was compared with baseline, placebo, or other intravenous antihypertensive agents in the settings of severe hypertension (1 study), preoperative cardiac surgery (1), perioperative cardiac surgery (1), and postoperative cardiac surgery (4). In a multicenter, randomized, double-blind, placebo-controlled study of the efficacy of clevidipine in treating preoperative hypertension, the mean reduction from baseline in mean arterial pressure was 31.2% with clevidipine and 11.2% with placebo (P < 0.001). In a randomized, open-label, prospective study involving separate comparisons of clevidipine with nitroglycerin, sodium nitroprusside, and nicardipine, the median total AUC for digression in systolic BP from the predetermined target range differed significantly between clevidipine and nitroglycerin (4.14 vs 8.87 mm Hg . min/h; respectively, P < 0.001) and between clevidipine and sodium nitroprusside (4.37 vs 10.5 mm Hg . min/h; P = 0.003), but not between clevidipine and nicardipine (1.76 and 1.69 mm Hg . min/h). Another study found no significant difference in efficacy in controlling BP during the 3-hour study period between clevidipine and sodium nitroprusside (AUC for mean [SD] arterial pressure, 106 [25] and 101 [28] mm Hg . min/h, respectively). Adverse events in these studies included atrial fibrillation (13.0%-36.1% clevidipine vs 12.0% placebo), nausea (5.0%-21.0% vs 12.0%, respectively), fever (19.0% vs 13.7%), insomnia (12.0% vs 6.1%), and acute renal failure (9.0% vs 2.0%). In the studies reviewed, only 1 case of chest discomfort in the setting of severe hypertension was considered a serious adverse event related to clevidipine therapy.

CONCLUSION

In the Phase III trials reviewed, clevidipine was effective in controlling BP in the settings of perioperative cardiac surgery and severe hypertension and was associated with minimal adverse effects.

Perioperative hypertension: a review of current and emerging therapeutic agents

Perioperative hypertension is a common problem encountered by anesthesiologists, surgeons, internists, and intensivists. Surprisingly, no randomized, placebo-controlled studies exist that show that the treatment of perioperative hypertension reduces morbidity or mortality. Nevertheless, perioperative hypertension requires careful management. While sodium nitroprusside and nitroglycerin are commonly used to treat these conditions, these agents are less than ideal. Intravenous beta blockers and calcium channel blockers have particular appeal in this setting.

Preparation and evaluation of ethyl [(18)F]fluoroacetate as a proradiotracer of [(18)F]fluoroacetate for the measurement of glial metabolism by PET

INTRODUCTION

Changes in glial metabolism in brain ischemia, Alzheimer's disease, depression, schizophrenia, epilepsy and manganese neurotoxicity have been reported in recent studies. Therefore, it is very important to measure glial metabolism in vivo for the elucidation and diagnosis of these diseases. Radiolabeled acetate is a good candidate for this purpose, but acetate has little uptake in the brain due to its low lipophilicity. We have designed a new proradiotracer, ethyl [(18)F]fluoroacetate ([(18)F]EFA), which is [(18)F]fluoroacetate ([(18)F]FA) esterified with ethanol, to increase the lipophilicity of fluoroacetate (FA), allowing the measurement of glial metabolism.

METHODS

The synthesis of [(18)F]EFA was achieved using ethyl O-mesyl-glycolate as precursor. The blood-brain barrier permeability of ethyl [1-(14)C]fluoroacetate ([(14)C]EFA) was estimated by a brain uptake index (BUI) method. Hydrolysis of [(14)C]EFA in the brain was calculated by the fraction of radioactivity in lipophilic and water fractions of homogenized brain. Using the plasma of five animal species, the stability of [(14)C]EFA was measured. Biodistribution studies of [(18)F]EFA in ddY mice were carried out and compared with [(18)F]FA. Positron emission tomography (PET) scanning using common marmosets was performed for 90 min postadministration. At 60 min postinjection of [(18)F]EFA, metabolite studies were performed. Organs were dissected from the marmosets, and extracted metabolites were analyzed with a thin-layer chromatography method.

RESULTS

The synthesis of [(18)F]EFA was accomplished in a short time (29 min) and with a reproducible radiochemical yield of 28.6+/-3.6% (decay corrected) and a high radiochemical purity of more than 95%. In the brain permeability study, the BUI of [(14)C]EFA was 3.8 times higher than that of sodium [1-(14)C]fluoroacetate. [(14)C]EFA was hydrolyzed rapidly in rat brains. In stability studies using the plasma of five animal species, [(14)C]EFA was stable only in primate plasma. Biodistribution studies in mice showed that the uptake of [(18)F]EFA in selected organs was higher than that of [(18)F]FA. From nonprimate PET studies, [(18)F]EFA was initially taken into the brain after injection. Metabolites related to the tricarboxylic acid (TCA) cycle were detected in common marmoset brain.

CONCLUSION

[(18)F]EFA rapidly enters the brain and is then converted into TCA cycle metabolites in the brains of common marmosets. [(18)F]EFA shows promise as a proradiotracer for the measurement of glial metabolism.

Clevidipine Butyrate Injectable Emulsion

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Treatment of acute severe hypertension: current and newer agents

Approximately 72 million people in the US experience hypertension. Worldwide, hypertension may affect as many as 1 billion people and be responsible for approximately 7.1 million deaths per year. It is estimated that approximately 1% of patients with hypertension will, at some point, develop a hypertensive crisis. Hypertensive crises are further defined as either hypertensive emergencies or urgencies, depending on the degree of blood pressure elevation and presence of end-organ damage. Immediate reduction in blood pressure is required only in patients with acute end-organ damage (i.e. hypertensive emergency) and requires treatment with a titratable, short-acting, intravenous antihypertensive agent, while severe hypertension without acute end-organ damage (i.e. hypertensive urgency) is usually treated with oral antihypertensive agents. The primary goal of intervention in a hypertensive crisis is to safely reduce blood pressure. The appropriate therapeutic approach of each patient will depend on their clinical presentation. Patients with hypertensive emergencies are best treated in an intensive care unit with titratable, intravenous, hypotensive agents. Rapid-acting intravenous antihypertensive agents are available, including labetalol, esmolol, fenoldopam, nicardipine and sodium nitroprusside. Newer agents, such as clevidipine and fenoldopam, may hold considerable advantages to other available agents in the management of hypertensive crises. Sodium nitroprusside is an extremely toxic drug and its use in the treatment of hypertensive emergencies should be avoided. Similarly, nifedipine, nitroglycerin and hydralazine should not to be considered first-line therapies in the management of hypertensive crises because these agents are associated with significant toxicities and/or adverse effects.

Perioperative hypertension management

Perioperative hypertension is commonly encountered in patients that undergo surgery. While attempts have been made to standardize the method to characterize the intraoperative hemodynamics, these methods still vary widely. In addition, there is a lack of consensus concerning treatment thresholds and appropriate therapeutic targets, making absolute recommendations about treatment difficult. Nevertheless, perioperative hypertension requires careful management. When treatment is necessary, therapy should be individualized for the patient. This paper reviews the pharmacologic agents and strategies commonly used in the management of perioperative hypertension.

New therapeutic perspectives with clevidipine: an ultra-short-acting intravenous Ca2+channel blocker

Intravenous antihypertensive agents are used in clinical situations in which the immediate, precise control of blood pressure is a clinical necessity. Clevidipine is a new, vascular-selective, dihyrdopyridine Ca(2+) channel blocker, which exerts its hemodynamic effects through selective arterial vasodilation without effects on the venous circulation. Because it is a potent coronary vasodilator, reduction in mean arterial pressure does not impair coronary perfusion. The unique properties of clevidipine include an ultra-short pharmacodynamic duration of action and a half-life after intravenous administration of approximately 2 min, resulting in very rapid onset and offset of antihypertensive effects. In clinical trials performed in patients undergoing cardiac surgery, clevidipine proved superior to nitroprusside and nitroglycerin in maintaining blood pressure within predetermined ranges during the perioperative period. Its safety profile is comparable to nicardipine and nitroglycerin and, in one study, was associated with reduced 30-day mortality compared with nitroprusside. Clevidipine constitutes a useful addition to available intravenous agents and could prove particularly valuable in circumstances that require the ability to rapidly terminate the blood pressure-lowering effects of administered agents.

Hypertensive crises: challenges and management

Hypertension affects > 65 million people in the United States and is one of the leading causes of death. One to two percent of patients with hypertension have acute elevations of BP that require urgent medical treatment. Depending on the degree of BP elevation and presence of end-organ damage, severe hypertension can be defined as either a hypertensive emergency or a hypertensive urgency. A hypertensive emergency is associated with acute end-organ damage and requires immediate treatment with a titratable short-acting IV antihypertensive agent. Severe hypertension without acute end-organ damage is referred to as a hypertensive urgency and is usually treated with oral antihypertensive agents. This article reviews definitions, current concepts, common misconceptions, and pitfalls in the diagnosis and management of patients with acutely elevated BP as well as special clinical situations in which BP must be controlled.

Pharmacodynamic, Pharmacokinetic and Clinical Effects of Clevidipine, an Ultrashort-Acting Calcium Antagonist for Rapid Blood Pressure Control

Clevidipine is an ultrashort-acting vasoselective calcium antagonist under development for short-term intravenous control of blood pressure. Studies in animals, healthy volunteers and patients have demonstrated the vascular selectivity and rapid onset and offset of antihypertensive action of clevidipine, a synthetic 1,4-dihydropyridine that inhibits L-type calcium channels. Clevidipine has a high clearance (0.05 L/min/kg) and is rapidly hydrolyzed to inactive metabolites by esterases in arterial blood. Its half-life in patients undergoing cardiac surgery is less than one min. Unlike sodium nitroprusside, a drug commonly used for the short-term control of blood pressure, which dilates both arterioles and veins, clevidipine reduces blood pressure through a selective effect on arterioles. As documented in animals and in cardiac surgical patients, clevidipine reduces peripheral resistance without any undesirable effect on cardiac filling pressure. It increases stroke volume and cardiac output. In anesthetized patients undergoing cardiac surgery clevidipine, unlike sodium nitroprusside, does not increase heart rate. In addition of having a favorable hemodynamic profile, suitable for rapid control of blood pressure, clevidipine protects against ischemia/reperfusion injuries, which are not uncommon during major surgery. In anesthetized pigs, clevidipine reduced infarct size after 45 min-long myocardial ischemia by 40%. In rats, renal function and splanchnic blood flow were better maintained when blood pressure was reduced with clevidipine than with sodium nitroprusside. Clevidipine was well tolerated in Phases I and II of clinical trials that included more than 300 individuals/patients. Since there are no known compounds with similar pharmacodynamic and pharmacokinetic properties in clinical development, it is anticipated that clevidipine, a compound tailored to the needs of anesthesiologists, has the potential to become a drug of choice for controlling blood pressure during surgical procedures.

HPLC enantiomer separation of a chiral 1,4-dihydropyridine monocarboxylic acid

An enantioselective anion exchanger based on tert-butylcarbamoylquinine as chiral selector and thiol-modified silica as chromatographic support was applied for the enantiomer separation of the shortacting calcium antagonist clevidipine after its hydrolysis to methyl 4-(2',3'-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate. This hydrolyzed derivative of clevidipine is the primary metabolite and precursor of the parent drug. Method development included the steps of optimization of the composition of the mobile phase (pH, type and content of organic modifier, polar organic mode), screening of various structural analogs of above mentioned CSP, and evaluation of the effect of the flow rate. These detailed studies gave insight into the operational mode of the CSP, which is basically an enantioselective anion exchange mechanism. The polar organic mode turned out to be advantageous with regard to enantioselectivity and resolution. The optimized method makes use of an eluent composed of 0.125% acetic acid in acetonitrile with flow rate of 1 ml/min at a constant temperature of 25 degrees C, and allows the separation of the both enantiomers with enantioselectivity alpha of 1.25 and a resolution RS of 3.0 within 10 min. On the above mentioned quinine carbamate phase the (R)-enantiomer is stronger retained, while a change to the corresponding quinidine carbamate CSP allows the reversal of the elution order.

Time-dependent cardioprotection with calcium antagonism and experimental studies with clevidipine in ischemic-reperfused pig hearts: part II

The intracellular calcium level is increased during ischemia and early reperfusion. The aim of this study was to study the role of the calcium influx in the development of myocardial ischemic and reperfusion injury during the early and late phases of ischemia and during early reperfusion. An ultrashort-acting calcium antagonist, clevidipine, was used as a tool for this investigation. Pentobarbital-anesthetized pigs were subjected to 45 minutes of LAD occlusion followed by 240 minutes of reperfusion. In the first set of experiments, clevidipine (0.3 nmol/kg per minute) was infused over 5 minutes into the ischemic myocardium via a catheter in the LAD, starting at 5, 35, or 44 minutes following the onset of ischemia (n = 6 in each group). The area at risk and the infarct size were determined after 240 minutes of reperfusion by staining with Evans blue dye and triphenyl tetrazolium chloride (TTC), respectively. In a second set of experiments, two groups of animals (n = 6 in each) were subjected to the same periods of ischemia and reperfusion; one group received no infusion during ischemia, whereas the other group received vehicle infusion during a 5-minute period between 5 and 10 minutes of ischemia. In the first set of experiments, there were no significant differences between the groups with regard to hemodynamic variables. The area at risk expressed as a percentage of the left ventricle was of similar magnitude in all three clevidipine-treated groups (about 18%). The infarct size, expressed as a percentage of the area at risk, was significantly smaller in pigs given clevidipine after 5 minutes (58 +/- 17%; p < 0.01) and after 44 minutes (42 +/- 6%; p < 0.01) of ischemia than in pigs receiving clevidipine after 35 minutes of ischemia (85 +/- 4%). The difference in infarct size between pigs given clevidipine after 5 or 44 minutes of ischemia was not significant. In the second set of experiments, there was a similar area at risk and no significant difference in infarct size between the noninfusion group and the 5-minute vehicle infusion group, indicating that the LAD infusion per se did not affect infarct size. The present results demonstrate that blockade of calcium influx by the short-acting dihydropyridine calcium antagonist clevidipine during the early phase of ischemia and at the time of reperfusion, but not during a late phase of ischemia, limits infarct size induced by ischemia and reperfusion. This indicates that the pathophysiological importance of calcium influx varies according to the different phases of myocardial ischemia and reperfusion.

Time-dependent cardioprotection with calcium antagonism and experimental studies with clevidipine in ischemic-reperfused pig hearts: part I

Clevidipine is a new ultrashort-acting dihydropyridine calcium antagonist developed for blood pressure regulation during cardiac surgery. When given locally to the ischemic and reperfused myocardium, clevidipine exerts a cardioprotective effect that varies depending on the timing of administration during ischemia. The current study explored the pharmacokinetics of clevidipine when administered locally into the coronary circulation. Pentobarbital-anesthetized pigs were randomly divided into four groups, of which three were subjected to myocardial ischemia through ligation of the left anterior descending coronary artery (LAD) for 15, 35, or 45 minutes (n = 4 in each group). The fourth group (n = 4) was not subjected to LAD occlusion and acted as nonischemic controls. Clevidipine (0.3 nmol/kg per minute) was infused over a period of 5 minutes through a catheter distal to the LAD ligation in the ischemic pigs, or at the corresponding site of the nonligated LAD in the nonischemic pigs. Following release of the LAD ligation, or in the nonligated group following the drug infusion, the pigs were subjected to 60 minutes of reperfusion. Simultaneous blood samples were obtained for analysis of clevidipine from the femoral artery and the coronary vein during reperfusion and during drug infusion in the nonischemic pigs. Blood samples for estimating the in vitro hydrolysis rate both in whole blood and in plasma were also obtained. In nonischemic hearts, clevidipine reached a steady state level in the coronary venous blood of about 30 nM during the infusion. The concentration declined almost to the detection limit (1 nM) within 3 minutes of the end of infusion. The mean blood clearance of clevidipine was calculated to be 0.17 l/min per kilogram, and the estimated half-life was 0.5 minute. In animals subjected to different periods of ischemia, very low levels of clevidipine were detected in the coronary venous blood only during the first 2 minutes of reperfusion. There were no detectable levels in the arterial blood at any time. Blood concentration profiles of clevidipine did not differ with the length of myocardial ischemia. The in vitro half-life in pig blood was 13 minutes, and the corresponding half-life in plasma was 111 minutes. At a dose known to exert cardioprotection when given as an intracoronary injection, the systemic concentration of clevidipine does not reach pharmacologically active levels. Clevidipine has an ultrashort blood half-life, and ischemic duration of up to 45 minutes does not seem to change the cardiac metabolism of this drug. Thus, it represents a pharmacological tool well suited for the study of time windows in cardioprotection. Moreover, considering the possibility of exerting myocardioprotection without any systemic effects, it could be an interesting compound to test in a clinical setting.

Metabolism of prostaglandin glycerol esters and prostaglandin ethanolamides in vitro and in vivo

Prostaglandin glycerol esters (PG-Gs) and prostaglandin ethanolamides (PG-EAs) are generated by the action of cyclooxygenase-2 on the endocannabinoids 2-arachidonylglycerol (2-AG) and arachidonylethanolamide, respectively. These novel eicosanoids may have unique pharmacological properties and/or serve as latent sources of prostaglandins at sites remote from their tissue of origin. Therefore, we investigated the metabolism of PG-Gs and PG-EAs in vitro and in vivo. PGE(2)-G was rapidly hydrolyzed in rat plasma to generate PGE(2) (t(1/2) = 14 s) but was only slowly metabolized in human plasma (t(1/2) > 10 min). An intermediate extent of metabolism of PGE(2)-G was observed in human whole blood (t(1/2) approximately 7 min). The parent arachidonylglycerol, 2-AG, and the more stable regioisomer, 1-AG, also were much more rapidly metabolized in rat plasma compared with human plasma. PGE(2)-EA was not significantly hydrolyzed in plasma, undergoing slow dehydration/isomerization to PGB(2)-EA. Both PGE(2)-G and PGE(2)-EA were stable in canine, bovine, and human cerebrospinal fluid. Human 15-hydroxyprostaglandin dehydrogenase, the enzyme responsible for the initial step in PG inactivation in vivo, oxidized both PGE(2)-G and PGE(2)-EA less efficiently than the free acid. The sterically hindered glyceryl prostaglandin was the poorest substrate examined in the E series. Minimal 15-hydroxyprostaglandin dehydrogenase oxidation of PGF(2 alpha)-G was observed. PGE(2)-G and PGE(2)-EA pharmacokinetics were assessed in rats. PGE(2)-G was not detected in plasma 5 min following an intravenous dose of 2 mg/kg. However, PGE(2)-EA was detectable up to 2 h following an identical dose, displaying a large apparent volume of distribution and a half-life of over 6 min. The results suggest that endocannabinoid-derived PG-like compounds may be sufficiently stable in humans to exert actions systemically. Furthermore, these results suggest that the rat is not an adequate model for investigating the biological activities of 2-arachidonylglycerol or glyceryl prostaglandins in humans.

Enantioselective pharmacokinetics of the enantiomers of clevidipine following intravenous infusion of the racemate in essential hypertensive patients

The aim of the study was to characterize the individual pharmacokinetics of (-)-R- and (+)-S-clevidipine following intravenous constant rate infusion of rac-clevidipine to essential hypertensive patients. Twenty patients received three out of five randomized treatments with clevidipine. The pharmacokinetics of the separate enantiomers were evaluated by compartmental analysis of blood concentrations vs. time curves using the population approach. The derived pharmacokinetic parameters were used to simulate the time for 50 and 90% postinfusion decline following various infusion times of rac-clevidipine. A two-compartment model was used to describe the dispositions of the enantiomers; there were only minor differences between the estimated pharmacokinetic parameters of the separate enantiomers. The mean blood clearance values of (-)-R- and (+)-S-clevidipine were 0.103 and 0.096 l/min/kg, and the corresponding volumes of distribution at steady state were 0.39 and 0.54 l/kg, respectively. The context-sensitive half-time was approximately 2 min regardless of stereochemical configuration, and a 90% decline in concentration was achieved approximately 8 min postinfusion for (-)-R-clevidipine and 11 min for (+)-S-clevidipine, following clinically relevant infusion times with clevidipine. In conclusion, both enantiomers are high-clearance compounds with similar blood clearance values. The volume of distribution for the enantiomers is slightly different, presumably due to differences in the protein binding. From a pharmacokinetic point of view, the use of a single enantiomer as an alternative to the racemic clevidipine will not offer any clinical advantages.

Clevidipine blockade of L-type Ca2+ currents: steady-state and kinetic electrophysiological studies in guinea pig ventricular myocytes

Steady-state and transient effects of clevidipine, a rapidly degraded dihydropyridine (DHP) L-type Ca2+ channel antagonist, were examined on I(Ca) in guinea pig ventricular myocytes. When myocytes were voltage-clamped with holding potential (V(H)) at -80 mV, 10 nM clevidipine decreased I(Ca) at 0 mV by approximately 30%, but >50% when V(H) was -40 mV. Rapid (<50 ms) perfusion switching and repeated depolarizations delivered at 0.5-2 Hz were used to determine the time constants of onset (tau(on)) and recovery from (tau(off)) clevidipine inhibition of I(Ca). The tau(on) and tau(off) were monoexponential functions of time. The tau(on) of I(Ca) inhibition decreased from 21.5 +/- 1.2 to 9.9 +/- 0.9 s when the rapidly applied [clevidipine] was increased from 10 to 100 nM at V(H) = -80 mV; tau(off) was independent of the applied [clevidipine] and was 23.9 +/- 1.1 s. The dissociation constant (K(D)) calculated for clevidipine at V(H) = -80 mV was 65 +/- 3 nM, similar to the IC50 of 78 nM determined in steady-state measurements. Decreasing V(H) to -40 mV increased tau(off) more than threefold to 81 +/- 6 s, and K(D) was markedly decreased to 9.0 +/- 0.8 nM (IC50, 7.1 nM at V(H) = -40 mV). The increased affinity at depolarized V(H) may contribute to the varying concentration-effect relation observed in vivo.

Pharmacokinetics and pulmonary extraction of clevidipine, a new vasodilating ultrashort-acting dihydropyridine, during cardiopulmonary bypass

Clevidipine is a new vascular-selective, calcium channel antagonist of the dihydropyridine type with an ester side chain susceptible to esterase metabolism. In healthy volunteers, it has high clearance (0.069 litres min-1 kg-1) with a small volume of distribution at steady state (0.19 litres kg-1). The half-lives of the two initial rapid phases, accounting for approximately 95% of the area under the curve after an i.v. bolus, are 0.7 and 2.3 min, respectively. The aims of this study were to determine the pharmacokinetics and the pulmonary extraction ratio of clevidipine in patients undergoing cardiac surgery. Seventeen patients received clevidipine as an i.v. infusion before cardiopulmonary bypass (CPB), and eight of these patients were also given clevidipine during hypothermic CPB. Mixed venous and arterial blood samples were taken for pharmacokinetic analysis and calculation of pulmonary extraction ratio. A two-compartment pharmacokinetic model with zero-order input was used to describe the pharmacokinetics of clevidipine before and during CPB. Virtually identical concentrations in mixed venous and arterial blood suggest negligible pulmonary metabolism of clevidipine. The total blood clearance of clevidipine is extremely high (0.055 litres min-1 kg-1). During CPB, clearance of clevidipine was significantly reduced, to 0.03 litres min-1 kg-1 (P < 0.005), probably as a consequence of reduced body temperature.

Calcium antagonist protects the myocardium from reperfusion injury by interfering with mechanisms directly related to reperfusion: an experimental study with the ultrashort-acting calcium antagonist clevidipine

To test the hypothesis that calcium antagonists protect the myocardium from reperfusion-induced damage by local myocardial mechanisms just at the time of reperfusion, the myocardioprotective effects of the dihydropyridine clevidipine were investigated, taking advantage of its ultrashort-acting effect. Pigs were subjected to 45 min of myocardial ischemia by occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. Either clevidipine (0.3 nmol/kg/min, n = 6) or the corresponding amount of vehicle (n = 6) was administered to the ischemic myocardium by retrograde coronary venous infusion over a 30-min period starting 10 min before reperfusion. Hemodynamic variables (heart rate, left ventricular systolic and end-diastolic pressure, max dP/dt, and mean arterial blood pressure) as well as coronary blood flow were measured throughout the experiment. At the end of reperfusion, the area at risk (percentage of left ventricle) was determined by infusion of Evans blue into the left atrium, and the infarct size, by triphenyl tetrazolium chloride (TTC) staining. The plasma level of endothelin-like immunoreactivity (ET-LI) was analyzed in blood from the aorta and the anterior coronary vein before ischemia and at different times during reperfusion. The area at risk was similar in the vehicle and the clevidipine groups. The infarct size, expressed as a percentage of the area at risk, was 80 +/- 9.2 in the vehicle group, whereas it was significantly reduced to 51 +/- 9.2% in the clevidipine group (p < 0.01). Clevidipine did not influence any of the hemodynamic variables measured throughout the study. A nonsignificant trend toward decreased total ET-LI overflow during 4-h reperfusion was observed in the clevidipine-treated pigs compared with vehicle-treated ones (5.3 +/- 1.4 vs. 7.1 +/- 3.4 pmol). These results demonstrate that, in this model of ischemia/reperfusion-induced myocardial infarction, clevidipine reduced the damage to the myocardium when given in association with reperfusion. The local administration of the compound together with its short blood half-life shows that clevidipine reduces reperfusion-induced damage by local mechanisms within the ischemic tissue rather than by peripheral mechanisms.

Clinical and pharmacokinetic results with a new ultrashort-acting calcium antagonist, clevidipine, following gradually increasing intravenous doses to healthy volunteers

AIMS

To investigate the tolerability and safety of clevidipine in healthy male volunteers during intravenous infusion at gradually increasing dose rates and to obtain preliminary information on the pharmacokinetics and pharmacodynamic effects of the drug.

METHODS

Twenty-five subjects were enrolled in the study and twenty-one of them were included twice, resulting in a total of forty-six study entries encompassing 20 min infusions of clevidipine at target dose rates ranging from 0.12 to 48 nmol min-1 kg-1. Haemodynamic variables and adverse events were recorded throughout the study. Concentrations of clevidipine and its primary metabolite, H 152/81, were followed in whole blood, and the pharmacokinetics were evaluated by non-compartmental and compartmental analysis. An Emax model was fitted to the effect on mean arterial pressure (MAP) over heart rate (HR) and the corresponding blood concentrations of clevidipine.

RESULTS

Clevidipine was administered up to a target dose rate of 48 nmol min-1 kg-1, where a pre-determined escape criterion was reached (HR>120 beats min-1 ) and the study was stopped. The most common adverse events were flush and headache, which can be directly related to the mechanism of action of clevidipine. There was a linear relationship between blood concentration and dose rate in the range studied. The median clearance value determined by non-compartmental analysis was 0.125 l min-1 kg-1. Applying the population approach to the sparse data on clevidipine concentrations, an open two compartment pharmacokinetic model was found to be the best model in describing the disposition of the drug. The population mean clearance value determined by this method was 0.121 l min-1 kg-1, and the volume of distribution at steady state was 0.56 l kg-1. The initial half-life, contributing by more than 80% to the total area under the blood concentration-time curve following i.v. bolus administration, was 1.8 min, and the terminal half-life was 9.5 min. At the highest dose rates, MAP was reduced by approximately 10%, and the HR reached the pre-determined escape criterion for this study (>120 beats min-1 ).

CONCLUSIONS

Clevidipine is well tolerated and safe in healthy volunteers at dose rates up to at least 48 nmol min-1 kg-1. The pharmacokinetics are linear over a wide dose range. Clevidipine is a high clearance drug with extremely short half-lives. The effect of clevidipine on the blood pressure was marginal, probably due to a compensatory baroreflex activation in this population of healthy volunteers. A simple Emax model adequately describes the relationship between the pharmacodynamic response (MAP/HR) and the blood concentrations of clevidipine.